Diagnosing Canine Cushing's Disease with an ACTH Stimulation Test

Canine Cushing’s disease is a condition where too much
cortisol is in the bloodstream. The complex system of pituitary gland,
hypothalamus and hormone secretions is broken, making the dog’s body
unable to regulate the cortisol production. The elevated cortisol
levels in turn have an impact on various body systems including nervous
system, cardiovascular system, skeletal muscles, blood sugar levels,
fat metabolism, kidney function and immune response. Once diagnosed,
Cushing’s disease can be treated, allowing the dog to live a more
comfortable life and avoiding the secondary problems caused by the
disease. While no single test can properly diagnose Cushing’s disease,
the ACTH stimulation test, used in tandem with other diagnostic
results, can pinpoint the diagnosis.

ACTH Stimulation Test

The ACTH stimulation test is conducted by comparing baseline blood
work against blood work taken 1 to 2 hours after an injection of the
ACTH hormone. ACTH is the hormone that is naturally produced in the
pituitary gland and triggers the release of cortisol from the adrenals
into the dog’s system. If the test results show an extremely elevated
level of cortisol in the bloodstream, it is likely the dog has
Cushing’s disease. The ACTH stimulation test is often done in
conjunction with a low dose dexamethasone suppression test in order to
confirm the diagnosis of Cushing’s disease.

Neither of these tests can differentiate between the different
causes of Cushing’s disease. In order to do this, a high dose
dexamethasone suppression test must be conducted. Baseline blood work
is compared to blood work at 4 and 8 hours after the dog has been given
a high dose of dexamethasone. The test results will determine the cause
of the Cushing’s disease and allow the veterinarian to prescribe the
appropriate treatment.

Treatment for Cushing’s Disease

Because most dogs diagnosed with Cushing’s disease are elderly and
already being treated for other medical conditions, treatment can be
complicated. For Cushing’s caused by adrenal tumors, surgical removal
of benign tumors can cure the disease. Malignant adrenal tumors often
go unrecognized until the tumor has already attached itself to the
liver or lungs. In these cases, non-surgical treatment is often the
route taken.

Medicinal treatment for pituitary dependent or for inoperable
adrenal-based Cushing’s disease is done, not to cure the disease, but
to make the dog’s quality of life more comfortable. Your veterinarian
will choose the drugs based upon your dog’s condition, the type of
Cushing’s present and other medications your dog may be on.

Iatrogenic Cushing’s is caused by medications that cause
overproduction of corticosteroids. Gradual withdrawal of the offending
medication will allow the dog’s body to fully recover and return to a
non-Cushing’s state.

The ACTH stimulation test allows your veterinarian to determine
whether or not your dog’s body is producing excessive amounts of
cortisol and creating a toxic situation that can affect a variety of
his body’s systems. Once the initial diagnosis is confirmed by
additional tests, and the cause of the Cushing’s disease identified,
treatment can begin, allowing your dog to live his life more
comfortably.